With communicating data through the Internet, there is a problem of preventing spoofing of a sender.
There has been proposed a known verification technique using an electronic signature in order to prevent the spoofing of the sender. For example, a known art proposes verification of the electronic signature. The known art verifies the electronic signature, which is included in a device certificate attached to electronic mail, using a certification authority certificate issued by a certification authority for authenticating the device certificate. The known art specifies an act of the spoofing of the sender by determining whether or not the device certificate is issued by the certification authority. Hereinafter, a certification authority certificate, which is issued by a certification authority that authenticates an electronic signature attached to an electronic mail, is referred to as a “specific certification authority certificate”.